With the industrial revolution there was a problem of kids in cities getting rickets. This was due to a lack of vitamin C and that was due to a lack of daylight due to the smog.

The solution was to take the kids out of the city so they could spend time in the countryside.

However, along with the industrial revolution came steam trains, and, with steam trains, it became a lot easier to get fresh food from the farm to the city table.

Milk became an early commodity for this railway trade, in the days before refrigeration. Bottling had to be invented too, along with pasteurisation to get the modern milk product. They fortified it with vitamin D and, in time, made it mandatory in schools for kids to have dinky bottles of milk for their morning break. All kids hated the stuff but it was 'good for them' and good for keeping farmers gainfully employed.

Then the clean air acts came along, with the first street to ban fires in fireplaces being opposite the smoke free coal factory, the factory being anything but smoke free. Deindustrialisation happened too, so there were no cities with smokestack industries at their heart.

With clean air there was no longer any need to fortify the milk with vitamin D, so that stopped. From now on, kids would get their vitamin D doing things such as playing in the school playground.

But then we became seriously car dependent and the age of the free-range child was over. With 'stranger danger' and screens (initially just TV) taking over, we entered a new era of people not getting enough daylight again.

Along the way vitamin D has been downgraded, much like Pluto, from being a 'vitamin' to being a hormone. A lot of people want to point this out and explain the science to you. From hearing how some talk about vitamin D, it sounds like the recommended supplements are all over the place.

Clearly there are millions, if not billions that seem to be living just fine with not much sunlight in their lives and on no vitamin D supplements. Where's the rickets? Good question, but then, in Antarctica, where there are months of darkness to endure, they are on something like 20,000 units a day, and they probably know what they are doing.

Maybe following their example for this winter could be my next 'nutrition experiment'. Sometimes, when there is so much conflicting information, it is best to do an n=1 experiment with one's own body.